In recent years, development aimed at reducing loss of a rotating electrical machine to enhance efficiency thereof has been actively made. One conceivable method for reducing the loss of the rotating electrical machine is to improve the ratio of a copper wire (coil) wound around a core to its winding space, that is, a so-called space factor, to thereby suppress heat generation of copper, that is, copper loss.
Note that, in a direct winding method for directly winding a coil around a core through intermediation of an insulating member, the coil cannot be wound in intimate contact with the core but bulges, and hence the coil cannot be effectively wound in a region to be wound around. In particular, this tendency is more remarkable as the coil becomes thicker, which is responsible for hindering the improvement of the space factor of the coil.
In view of this, the following method is known to deal with such a case. That is, the coil is wound temporarily around a spool prepared separately, and after that, a bulging portion of the coil is externally shaped to correct the bulge, and the coil is then inserted onto the core. The use of such assembling step can improve the space factor of the coil.
As another method for further improving the space factor of the coil, it has been proposed to apply an edgewise coil. The edgewise coil is formed by bending a rectangular wire having a rectangular conductor cross-section in such a direction that the short side of the conductor cross-section is located on an inner side of the axis of the coil.
The use of the edgewise coil can eliminate an unnecessary gap to improve the space factor of the coil as compared to the use of a round wire having a circular conductor cross-section. Besides, the edgewise coil has a single layer structure for the core, and hence, as compared to a round wire to be wound into a plurality of layers, heat can be directly dissipated to the core to improve heat dissipation performance.
The following method has been proposed for the edgewise coil as well. That is, after the edgewise coil is formed once, the edgewise coil is inserted onto the core through intermediation of an insulator, to thereby manufacture a stator (see, for example, Patent Literature 1).